Utilities provide for water, gas or electrical energy on a continuous basis and via suitable transmission and distribution systems. The latter include sites, such as sources and substations, which have to be coordinated in one way or the other across distances of hundreds of kilometers. Within utility communication systems that are associated with the distribution systems, a variety of messages are exchanged over long-distance communication links between distant sites of the utility in order to safely transmit and distribute water, gas or electrical energy.
For securely transmitting messages over long distances from one site to the other, the utility may revert to a Wide-Area communication Network (WAN). In the present context, a WAN can be a dedicated point-to-point communication link between two sites based on for example optical fiber or pilot wires, a connection-oriented communication network with a guaranteed data rate such as Ethernet over SDH/HDLC, or a packet-oriented communication network interconnecting a number of sites of the utility, and including a plurality of specific network elements such as switches, repeaters and possibly optical transmission media at the physical layer.
Electric power utilities can rely on connection-oriented or circuit-switched SDH (Synchronous Digital Hierarchy) or SONET (Synchronous Optical Networking) networks for communication of mission critical operation data like teleprotection signaling or SCADA (Supervisory Control and Data Acquisition) control and supervision data. This technology features proven quality of service and path resilience of less than 50 ms, for example, in case of a failure of an optical link. Further, it can be possible to predefine the data path that a particular communication service shall follow inside the network, which is referred to as ‘traffic-engineering’ in the following.
FIG. 1 depicts a communication network with a meshed topology according to a known implementation. Namely, FIG. 1 shows an exemplary communication network with a meshed topology or structure as often found in utility networks, in which nodes 1 to 5 and links a to g form a plurality of loops. Each node is connected to at least two neighboring nodes of the meshed network as well as to client or end devices (not shown) running utility applications that communicate over the network. While in this topology the normal traffic path for data between node 1 and 3 is through the link a-b, SDH and SONET systems are capable of switching this traffic to for example links c-g-f within 50 ms, for example, in case of a fiber link failure in link a. An important prerequisite in order to enable this path switchover is the traffic engineering, which allows the user to predefine the working path of the communication service, e.g., link a-b, and equally to predefine the protecting path for these services, e.g., links c-g-f, and to configure the nodes to handle traffic accordingly.
In another known implementation, and as an alternative to the above-mentioned connection-oriented communication network, the Wide Area communication Network (WAN) may be a packet-switched communication network, such as an Ethernet (Layer-2 of the OSI communication stack) network or an IP (Layer-3) network with a number of interconnected switches or routers as the nodes. In the context of the present disclosure, the difference between a Local Area Network (LAN) and a WAN is considered to reside in the geographical extension rather than in the network topology, with WAN inter-node distance in excess of 10 km, for example, as opposed to LANs restricted to individual premises or utility substations.
In known communication systems technology implementations, within any Local Area Network (LAN) constructed by connecting a plurality of computers or other intelligent devices together, a concept called “virtual LAN” (VLAN) employs functionality for grouping terminals or nodes which are connected to switches of the network. Ethernet VLANs according to IEEE 802.1Q allow restricting access to the terminals connected to an Ethernet network within a VLAN as well as restricting the data flow of multicast Ethernet messages to predefined parts of the Ethernet network to which receiver terminals belonging to the same VLAN are connected.
In known Ethernet switch-based networks VLAN definitions can be handled within the Ethernet switches, therefore the latter have to be configured or otherwise made aware of the relevant VLANs. Furthermore, it is assumed that any single connected terminal belongs to one specific VLAN. This terminal can then communicate with other terminals belonging to the same VLAN. When configuring the switches, the port to such single-connection terminal is therefore called access port, and this access port should be allowed to belong to one VLAN, while the other ports internal to the communication system, called trunk ports, may belong to several VLANs.
A recently introduced standard entitled Parallel Redundancy Protocol (PRP, IEC 62439-3 Clause 4) provides for seamless redundancy and switchover for Ethernet based communication systems with two redundant, e.g., fully duplicated, Ethernet networks. Ethernet traffic entering a PRP capable node is duplicated by this node and sent to a destination node via the two redundant networks. The destination node undoes the redundancy by accepting the first of the duplicated packets and by discarding the redundant packet that in normal operation arrives at a later time. By duplicating the traffic and sending it over two distinct networks, the failure of any network link in the system does not interrupt or delay the traffic between the sender and receiver node.
While PRP is a viable solution for LANs, the erection of fully redundant wide-area utility communication networks with suitably duplicated network elements is neither a practical nor an economical solution. For example, where the utility already owns and operates a communication network with non-redundant links, subsequent duplication of for example optical fiber links is not appealing.